1. Field of the Invention
The present invention generally relates to a bioelectric impedance measuring apparatus, and more particularly to a bioelectric impedance measuring circuit for supplying electric current to and measuring bioelectric impedance of an organism.
2. Description of the Related Art
There is known a body fat measuring system that measures the percentage of body fat of an organism by measuring the bioelectric impedance of the organism (see, for example, Japanese Laid-Open Patent Application No. 2001-161655).
FIG. 5 is a block diagram showing a configuration of a body fat measuring system 10 according to a related art case.
The body fat measuring system 10 includes a CPU 11, a passive filter 12, a voltage/current converting circuit 13, electrodes 14, 15, a voltage detecting circuit 16, an input apparatus 17, and a display apparatus 18.
The CPU 11 is for outputting a square wave(s) according to a measurement start instruction (instruction to start measurement) from the input apparatus 17. The square wave output by the CPU 11 is supplied to the passive filter 12. The passive filter 12 shapes (waveform shaping) the supplied square wave into a sine wave (sinusoidal wave). The waveform-shaped sine wave is supplied to the voltage/current converting circuit 13.
The voltage/current converting circuit 13 converts (transforms) the sine wave received from the passive filter 12 into electric current and supplies the converted electric current to an organism from the electrode 14. The current supplied by the electrode 14 flows to ground via the electrode 15.
The voltage detecting circuit 16 detects the voltage of the electrode 14 and supplies the voltage to the CPU 11. The CPU 11 measures the bioelectric impedance of the organism based on the amplitude of the voltage supplied from the voltage detecting circuit 16, to thereby obtain, for example, the percentage of fat of the organism. The measurement result of the CPU 11 is supplied to the display apparatus 18 and displayed by the display apparatus 18.
Thus, in a bioelectric impedance measuring circuit according to a related art case, a passive filter is used for converting a square wave from a CPU into a sine wave. Since the passive filter requires a relatively large inductor and a capacitor, it cannot be included (mounted) in a semiconductor integrated circuit.